Both Nectar and Tesco Clubcard have a great range of partners for days out which cover many of the major attractions of the UK. Although the research couldn't check every deal it was worth pointing out that all the examples I encountered showed that Tesco was significantly more generous than Nectar for all these days out offers. This is an area where Tesco comes out miles ahead of Nectar even before the devaluation.
Here's a few examples:
Alton Towers and Thorpe Park
A day pass at Thorpe Park would cost £49.99 on the door, Alton Towers is £50.40. Nectar has a double up offer so you'd need £25 of Nectar points for admission (this is £5000 Sainsbury's spend at the new rates or £2500 spend on most other partners). Tesco just needs £12.50 in Clubcard points which would require £1250 spend, a quarter that of Sainsbury's.
Want to join English Heritage for access to many historic attractions? Sainsbury's offers annual membership for £40 on Nectar points (£8000 Sainsbury's spend) and Tesco offers it for £16.50 in Clubcard points meaning a spend of £1650.
The Merlin Annual Pass
The Merlin Annual pass gets you access to a number of Merlin attractions including theme parks such as Alton Towers and Thorpe Park, the SeaLife centres, the London Eye, the Dungeons, Legoland and Madame Tussauds.
Nectar has a double up offer so to pay for the pass worth £170 you need £85 worth of Nectar points. With Clubcard you only need £50 worth of Clubcard points for the pass.
So to get the pass you'd need to spend £17,000 (!) at Sainsbury's new earning rate or £8500 at other Nectar partners. With Tesco Clubcard you need to spend £5000.
Nectar offers a very poor deal in the days out category. For things such as Theme Parks it might be a better deal booking your tickets online in advance.